The stretch from 26 Sept to 3 Oct overlaps with your likely fertile window, if your cycle runs close to 28 days. Ovulation usually falls around day 14 after your last period on 10 Sept. Withdrawal doesn't fully prevent pregnancy, since sperm can be present before ejaculation happens. It's too late now for emergency contraception, since that only works within a few days of exposure.
Next Steps
Your period is due in the next week or so, going by a 28-day cycle. If it doesn't come on time, take a home urine
pregnancy test a few days after the missed date for an accurate result. Testing earlier can give a false negative.
Health Tips
If your cycles are often irregular, these date estimates may be off and a test could still read negative too early. Please see a gynaecologist if you miss your period or want more certainty on timing.